Steam treatment of polyamides



y 9, 1939- J. a MILES. JR 2, 17

STEAM TREATMENT OF POLYAMIDFIS Filed Feb. 15, 193'? STEAM AT 1EUD SYNTH ETIE PDLYAMIDE FILAM ENTS FIE. E.

EIJLD DRAWING EIY UNWINDINEI FREIM SLDWER-REV'EILVINE EDEJEIN TD FAETER-REVDLV! NEI EaElEuEalN John E1. Miles, JP.

Patented May 9, 1939 UNITED STATES PATENT OFFICE STEAM TREATMENT OF POLYAMIDES Application February 15, 1937, Serial No. 125,941

15 Claims.

This invention relates to synthetic linear condensation polyamides, and particularly to a process for improving the properties of shaped objects prepared from fiber-forming synthetic n linear condensation polyamides.

In my application filed on even date herewith, Serial No. 125,940,-and in application Serial No. 125,939, filed on even date herewith by V. R. Hardy and myself, there is disclosed the steam I" treatment of synthetic polyamide fibers as one of a combination of steps in a process for making polyamide wool-like fibers. The treatment of fiber-forming polyamides, however, with steam is not limited as to utility to such treatment of the i polyamides after they have been formed into fibers but is of wider application in that improvements in the manufacture of the fibers from the polyamides are brought about, and in that improved shaped articles of various kinds 20 may be made due to the fact that the steam treatment confers on such objects valuable properties which cannot otherwise be obtained.

An object of this invention is to improve the properties of shaped articles prepared from 25 fiber-forming synthetic linear condensation polyamides. Another object is to improve the utility of filaments and the like derived from synthetic linear condensation polyamides. Other objects will appear hereinafter.

so The synthetic fiber-forming polyamides to which the process of this invention is applied, and from which the improved products disclosed herein are made, are described in detail as to their preparation and properties in application 35 Serial Number 548,701, filed July 3, 1931; Serial Number 180, filed January 2, 1935; and Serial number 74,811, filed April 16, 1936. These fiberiorming polyamides are 01 two types, those derived from suitable diamine-dibasic acid mix- 40 tures or their equivalents, and those derived from polymerizable monoaminomonocarboxyllc acids or their amide-forming derivatives. These polyamides can be formed into films, sheets, and the like. They may, for example, be spun into filaments which yield oriented fibers of good quality on application of stress, herein referred to as "cold drawing. The cold drawn fibers show definite orientation along the fiber axis whereas the undrawn filaments are substantially unoriented. The term filament as used herein will refer to both oriented and unoriented filaments or threads which are drawn from the fiber-forming polymers regardless 01 whether the filaments or threads are low (continuous) or 55 short (staple), while the term "fiber will reier more specifically to the oriented filaments which are useful in the manufacture of yarn and fabric as are natural textile fibers. The term superpolyamide" will be used to designate a linear condensation polyamide capable of yielding useful fibers.

Although polyamide fibers as compared with other types of synthetic fibers are relatively insensitive to moisture in the sense that they are not very hygroscopic and have practically the same strength when wet as when dry, I have discovered that their properties are afiected in a remarkable way by steam. This applies not only to the oriented fibers but also to unoriented filaments and to shaped superpoiyamide objects in general. The term shaped object" or shaped article is used to indicate an article which has been formed into a useful shape. For the most part such articles will have a definite predetermined shape or form imparted by some process, such as spinning, casting, molding, or the like. Steam treatment has been found to improve the properties of the superpolyamide shaped objects in a number of ways. For example, when applied to crimped or wool-like polyamide fibers it renders the crimp much more permanent. It is very surprising in this connection that an improvement in crimp retentivity is obtained regardless of whether the steam treatment is ap plied to a preformed crimped polyamide fiber or to a fiber before the crimp is formed therein. The term crimped fiber is used herein to indicate that the fiber contains a crimp, crinkle, curl, spiral, helix, or serration regardless of whether the crimp or deformation is in one plane or in more than one plane as in the case of a curl or helix.

Another valuable application of this invention resides in improvements made possible in converting the superpolyamides into filaments and fibers. Thus, when applied to undrawn filaments, a short steam treatment improves their drawability, i. e., the ease with which the filaments are cold drawn into oriented fibers. In general, the recovery of shaped superpolyamide objects from deformations is improved by steam treatment.

The process of this invention consists in subjecting a shaped superpolyamide article, such as a filament, fiber, film, or molded product, to the action of steam. The best results are obtained with the use of saturated steam, the optimum conditions of time and temperature depending upon the nature of the superpolyamide article and the magnitude and nature of the efl'ect desired. Treatment with steam for prolonged periods, e. g., longer than two hours, should generally be avoided. The temperature selected should be below the melting point of the superpolyamide, temperatures ranging from 200 0., and preferably 100-150 (1., being employed with greatest advantage. When the ob- Ject of the steam treatment is to improve the retentivity of the crimp in wool-like polyamide fibers or to prepare polyamide fibers which will have good crimp retentivity on crimping. e. g.,

by the method described in the above mentioned copending application by V. R. Hardy and myself, a 20 minute treatment with saturated steam at C. is usually sufllcient. When the object is to improve the drawability of filaments, films, ribbons, etc., shorter treatment with steam is employed.

To illustrate the magnitude of the effect produced by steam, reference may be made to the improvement in crimp retention of wool-like polyamide fibers so treated. The permanency of the crimp, which I express in terms of "crimp recovery from stretch, can be determined empirically as follows. The crimped fibers are stretched until the crimps are just straightened out and then an additional 10% stretch based on the length of the straight fiber is applied. The fiber so stretched is then immersed in boiling water for 30 seconds, removed from the water, and allowed to dry for 2 minutes. The recovered crimp length is then measured. The crimp recovery from stretc may then be obtained in per cent by multiplying by 100 the quotient obtained by dividing the difference between initial straight length and recovered crimped length by the difierence between initial straight length and initial crimped length. Crimped polyamide fibers which have been treated with steam often have from five to ten times as good crimp recovery from stretch as untreated crimped fibers. This is illustrated by Example I.

Short steam treatment of superpolyamides, as previously mentioned, is of value in improving the drawability of polyamide filaments. As already indicated, a remarkable property of polyamide filaments is that they can be cold drawn, i. e., elongated by application of stress at temperatures below the melting point, and thereby converted into oriented fibers which are superior to the undrawn filaments for use in fabrics and the like. It has now been found that undrawn filaments which have been treated with steam for a short time can be cold drawn with much less force than untreated filaments. This is particularly valuable when working with large filaments such as are designed for use as bristles. In these larger filaments the force required to draw the filaments at ordinary speed of drawing may be sufiicient to break them rather than cold draw them. In other words, steam treatment permits the cold drawing of larger filaments than is possible without steam treatment. This is not merely a temperature effect for if the steam treated filaments are cooled they still draw more easily than untreated filaments. Moreover, dry heat alone does not bring about a comparable change. It is within the scope of this invention to treat the filaments with steam during cold drawing. Steam appears to bring about some fundamental change in the shaped superpolyamide object, possibly a change in the crystalline structure.

The ability of shaped superpolyamide objects to recover from deformation is also improved by steam treatment. In the case of crimped fibers, this improved recovery is manifested by improved crimp retentivity. By virtue of this improved crimp retentivity the crimped fibers have improved resiliency.

In the diagrammatic views of the accompanying drawing:

Fig. 1 illustrates in elevation apparatus suitable in one method for applying to synthetic polyamide filaments the new steam treatment step of this invention; and

Fig. 2 shows in elevation suitable mechanism for cold drawing the polyamide filaments into oriented fibers.

In Fig. 1, -the numeral i indicates the steam supply line to a vessel 2 of any suitable design within which are the polyamide filaments 3 wound around a bobbin 4. The filaments are conveniently cold drawn by the means shown in Fig. 2 which consists in transferring the filaments from the slower revolving bobbin 5 to the faster revolving bobbin Ii. This cold drawing step is not new per se but is preferably applied in conjunction with the new steam treatment described herein, the cold drawing step, as will appear in the examples, being applied before, after, or during the steam treating step.

This invention is described more specifically in the following examples.

Example I The superpolyamide, polydecamethylene adipamide, used in this example was prepared by heating 2 mols of decamethylene diammonium adipate (the salt derived from decamethylenediamine and adipic acid) and 0.07 mol of adipic acid (viscosity stabilizer) for 2 hours at 265 C. under 100 lbs. per square inch pressure applied with oxygen-free nitrogen and then for one hour at atmospheric pressure. The polymer had an intrinsic viscosity of 0.74, where intrinsic viscosity is defined as log), C

in which Ar is the viscosity of a dilute m-cresol solution of the polymer divided by the viscosity of m-cresol in the same units and at the same temperature, and C is the concentration in grams of polymer per 100 cc. of solution. This superpolyamide was then spun from melt at a temperature of about 240 C. under a pressure of lbs. per square inch, applied with oxygen-free nitrogen, at a spinning rate of 600 ft. per minute, through a spinneret having 10 orifices each 0.0078 inch in diameter, placed at the bottom of 0.125 inch cone-shaped protrusions extending outward from the delivery side of the spinneret. The. filaments were collected on a motor driven drum without appreciable tension. After aging for several hours at ordinary temperature the filaments were wet with water and cold drawn by winding them on a second drum having a peripheral speed 2.75 times that of the first drum. The tension on the wet fibers was then released by unwinding them from the drum. As the released fibers dried, they crimped spontaneously as described more fully in the mentioned copending application by V. R. Hardy and myself. Although these fibers contained more than 10 crimps per inch and were quite wool-like in appearance, their crimp recovery from stretch as defined above was rather low (approximately 10%). When these crimped fibers were treated with saturated steam at 120 C. for 20 minutes, the crimp recovery from stretch was increased to 76%. The crimped fibers had a tenacity of 2.5 g. per denier based on the denier at break and were very useful in the preparation of woollike yarns and fabrics.

As shown by the following example, the steam treatment for producing permanent crimps may be applied to the filaments before releasing the tension, that is, before the crimp is put into the fiber.

Example I! Polyhexamethylene adipamide of intrinsic viscosity 0.81 was spun from melt at approximately 277 C. under a pressure of 150 lbs. per square inch applied with oxygen-free nitrogen using a spinneret of the type described in Example I. The filaments were collected on a motor driven bobbin. These filaments. which were substan tially unoriented and had a denier of about 18, were then soaked in water for several hours and cold drawn by winding them around a second bobbin which was kept wet and had a peripheral speed 2.75 times that of the first bobbin. This corresponds to 175% cold drawing. The fibers obtained in this way had a denier of 6.5. They were treated without being allowed to dry with saturated steam at 120 C. for 20 minutes and then removed from the bobbin. The released fibers crimped spontaneously when allowed to dry. Although these fibers lost most of their crimp when immersed in water, the crimp reappeared on drying so that the crimp recovery from stretch was approximately 95%, whereas crimped fibers similarly prepared but not subjected to steam treatment at any stage in their preparation had a crimp recovery from stretch of less than 10%.

The following example shows the value of the present process in forming large diameter filaments, e. g., bristles, from the polyamides:

Example III Polyhexamethylene adipamide of intrinsic viscosity 0.91 was formed from melt into filaments having a diameter of 0.032 inch. It was practically impossible to cold draw these large filaments due to breakage. When the filaments were first treated with steam at 120 C. for a short time, they were readily cold drawn without breakage. This was true even when the steam treated filaments were allowed to cool before cold drawing.

In the case of another sample of polyhexamethylene adipamide it was found that the force required to cold draw a filament of 0.026 inch diameter was 3.2 lbs., whereas the force required to cold draw a similar filament oi the same diameter, which had been steamed for a short time and then allowed to cool, was only 2.1 lbs.

The examples illustrate the steam treatment of shaped objects prepared from polydecamethyl ene adipamide and polyhexamethylene adipamide. Shaped objects derived from other superpolyamides can be rendered more useful by steam treatment in a similar way. A valuable class of superpolyamides for the preparation of the shaped objects mentioned herein are those derived from diamines of formula NHzCHzRCI-IzNI-Iz and dicarboxylic acids of formula HOOCCHzR'CHzCOOH or their amide-forming derivatives, in which R and R are divalent hydrocarbon radicals free from olefinic and acetylenic unsaturation and in which R has a chain length of at least two carbon atoms. An especially valuable group of superpolyamides within this class are those in which R is (CH1): and R is (CI-11),, wherein a: and y are integers and :r is at least two. As examples of superpolyamides which fall within one or both of these groups might be mentioned polytetramethylene adipamide, polytetramethylene suberamide, p'olytetramethylene sebacamide, polypentamethylene sebacamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polyoctamethylene adipamide, polydecamethylene adipamide, polydecamethylene p-phenylene diacetamide, and poly-p-nlylene sebacamide. As already indicated, this invention is also applicable to the treatment of shaped objects derived from polymerizable monoaminomonocarboxylic acids or their amide-forming derivatives. As examples of such superpolyamides might be mentioned the polymers derived from B-aminocaproic acid, 9-aminononanoie acid, and i1- aminoundecanoic acid. This invention is also applicable to the treatment of shaped objects derived from a mixture of superpolyamides or from interpolyamides oi co-polymers, i. e., polyamides prepared from a mixture of polyamideforming reactants, e. g., a mixture of two diamines with one or more dicarboxylic acids, or a mixture of a diamine, a dicarboxylic acid, and an amino acid.

This invention is not limited to the steam treatment of shaped objects consisting solely of superpolyamides. Other materials, such as plasticizers, e. g., o-hydroxydiphenyl, delusterants, e. g., titanium dioxide, pigments, extenders, fillers, dyes, resins, oils, cellulose derivatives, and the like may be present in addition to the superpolyamide. Thus a delustered crimped polyamide fiber containing 2% of titanium dioxide develops excellent crimp retentivity on treatment with saturated steam. The foreign material, when present in moderate amounts, does not interfere with the beneficial eifect of the steam.

As already indicated, it is desirable to use saturated steam in the application of this inven tion. It is within the scope of this invention, however, to use steam which is not saturated; in fact, steam may be employed under reduced pressure and may be mixed with inert gases. When this procedure is followed temperatures below 100 C. can be used, but temperatures above 100 C. are more desirable. When operating at high temperatures, it is usually desirable to exclude oxygen from the steam. The most rapid and pronounced eii'ects are obtained with the use of saturated steam under pressure. It is within the scope of this invention to subject the shaped superpolyamide articles to intermittent steam treatment.

In view of the fact that the superpolyamides yield especially useful filaments and fibers, the application of this invention to shaped objects of this type has been emphasized. When working with such products, it is desirable to apply the steam treatment to the filaments, fibers, or yarns before they are formed into a fabric, but the treatment of the fabric itself with steam is not precluded. Thus. steam treatment may be used in the finishing treatment applied to superpolyamide fabrics, particularly those prepared from crimped fibers. Steam treatment can also be applied with beneficial results to superpolyamide ribbons, foils, films. sheets, and even molded objects.

It will be evident from the foregoing discussion that this invention provides a simple and economical process for improving the properties oi shaped articles derived from fiber-forming synthetic linear condensation polyamides. The invention is applicable to a variety of such prod- 5 note, the magnitude oi the efiect produced depending somewhat upon the form or shape oi the product and upon the duration of the steam treatment. The invention is applied with greatest advantage to filaments and fibers including those 10 which are short (staple) as well as those which are long (continuous). Among the beneficial results produced by state may be mentioned improved recovery from deformation (particularly oi fibres and bristles). improved crimp retention (or wool-like products). improved drawabiiity (of undrawn filaments) in the case of very short steam treatments, and improved crease retention (oi fabrics).

As many apparently widely diflerent embodiments oi this invention may be made without departing from the spirit and scope thereof, it istobeunderstoodthatldonotlimitmyselito the specific embodiments thereof except as defined in the appended claims.

I claim:

1. In a process for manufacturing improved shaped articles from fiber-forming synthetic polyamides, the step which comprises treating the article formed from said polyamides with a steam.

2. Thestepinthe pmcessset iorthin claiml in which the steam is saturated and ate temperature of 100 to 200 C.

3. In a process for improving the crimp retentivity oi crimped fibers comprising a synthetic linear poiyamide. the step of treating said crimped polyamide fibers with steam.

4. In a process for improving the properties of fibers obtained from synthetic linear poiyamides by forming a filament from the polyamide and stretching the filament, the new step comprising treating the filament bei'ore stretching with steam 5. a proces for improving the properties oiorientedfibersobtainedbyaprocesscomprising stretching filaments of synthetic linear condensation polyamides, the new step which comprises treating the filaments with steam during the stretching.

8. A process for improving the properties oi fibers from synthetic linear polyamides which comprises treating the fibers with steam.

7. The process step set forth in claim 1 wherein said fiber-forming synthetic polyamides are those obtainable by condensation polymerization from diamines and dicarboigvlic acids.

8. In a process for manufacturing improved shaped articles from a fiber-forming polyamide comprising polyhexamethylene adipamide, the step 01' treating said shaped articles with steam.

9. The process step set forth in claim 3 wherein said synthetic linear poLvamide is one obtainable by condensation polymerization from a diamine and a dicarboxylic acid.

10. The process step set forth in claim 3 wherein said polyamide is polyhexamethylene adipamide.

11. The process step set forth in claim 6 wherein said synthetic linear polyamides are those obtainable by condensation polymerization from diamines and dlcarboxylic acids.

12. A process for improving the properties of fibers from a polyamide comprising polyhexamethylene adipamide which comprises treating said fibers with steam.

13. In a process for improving the properties of fabrics formed from fiber-forming synthetic polyamldes, the step which comprises treating said fabric with steam.

14. The process step set forth in claim 1 wherein said fiber-forming synthetic poiyamides are those obtainable by polymerization of monoaminomonocarboxylic acids.

15. The procms step set forth in claim 6 wherein said synthetic linear polyamides are those obtainable by polymerization of monoaminomonocarboxylic acids.

JOHN B. MILES. Jr.

CERTIFICATE OF CORRECTION.

Patent KO.

JOHN B. MILES, J'R.

It is hereby certified that error appears in the printed specification oi! the above numbered patent requiring correction as follows: Page 3 secand column, line 21;, for the word'of" read or; and that thesaid Letters Patent should be read with this correction therein that the some may cone mm to the reco'rd or the case in the Patent (Ji'fice.

Signed and sealed this 20th day of June, A. D. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

economical process for improving the properties oi shaped articles derived from fiber-forming ayntheflc linear condensation polyamides. The invention is applicable to a variety of such products, the magnitude oi the efi'ect produced depending somewhat upon the form or shape oi the product and upon the duration of the steam treatment. The invention is applied with greatest advantage to filaments and fibers including those which are short (staple) as well as those which are long (continuous). Among the beneficial results produced by state may be mentioned improved recovery from deformation (particularly oi fibres and bristles). improved crimp retention (or wool-like products). improved drawabiiity (oi undrawn filaments) in the case of very short steam treatments, and improved crease retention (oi fabrics).

As many apparently widely diflerent embodiments oi this invention may be made without departing from the spirit and scope thereof, it istobeunderstoodthatldonotlimitmysclito flie specific embodiments thereof except as defined in the appended claims.

I claim:

1. In a process for manufacturing improved shaped articles from fiber-forming synthetic polyamides, the step which comprises treating the article formed from said polyamides with steam 2. Thestepinthe pmcessset iorthin claiml in which the steam is saturated and at'a temperature of 100 to 200 C.

3. In a process for improving the crimp retentivity oi crimped fibers comprising a synthetic linear polyamide. the step of treating said crimped polyamide fibers with steam.

4. In a process for improving the properties of fibers obtained from synthetic linear poiyamides by forming a filament from the polyamide and stretching the filament, the new step comprising treating the filament bei'ore stretching with steam 5. a proces for improving the properties oiorientedfibersobtainedbyaprocesscomprising stretching filaments of synthetic linear condensation polyamides, the new step which comprises treating the filaments with steam during the stretching.

8. A process for improving the properties oi fibers from synthetic linear polyamides which comprises treating the fibers with steam.

7. The process step set forth in claim 1 wherein said fiber-forming synthetic polyamides are those obtainable by condensation polymerization from diamines and dicarboigvlic acids.

8. In a process for manufacturing improved shaped articles from a fiber-forming polyamide comprising polyhexamethylene adipamide, the step 01' treating said shaped articles with steam.

9. The process step set forth in claim 3 wherein said synthetic linear polvamide is one obtainable by condensation polymerization from a diamine and a dicarboxylic acid.

10. The process step set forth in claim 3 wherein said polyamide is polyhexamethylene adipamide.

11. The process step set forth in claim 6 wherein said synthetic linear polyamides are those obtainable by condensation polymerization from diamines and dlcarboxylic acids.

12. A process for improving the properties of fibers from a polyamide comprising polyhexamethylene adipamide which comprises treating said fibers with steam.

13. In a process for improving the properties of fabrics formed from fiber-forming synthetic polyamldes, the step which comprises treating said fabric with steam.

14. The process step set forth in claim 1 wherein said fiber-forming synthetic poiyamides are those obtainable by polymerization of monoamincmonocarboxylic acids.

15. The procms step set forth in claim 6 wherein said synthetic linear polyamidos are those obtainable by polymerization of monoaminomonocarboxylic acids.

JOHN B. MILES. Jr.

CERTIFICATE OF CORRECTION.

Patent KO.

JOHN B. MILES, J'R.

It is hereby certified that error appears in the printed specification oi! the above numbered patent requiring correction as follows: Page 3 secand column, line 21;, for the word'of" read or; and that thesaid Letters Patent should be read with this correction therein that the some may cone mm to the reco'rd or the case in the Patent (Ji'fice.

Signed and sealed this 20th day of June, A. D. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents. 

